Side-Scan_Sonar backscatter tiles for Hudson River, NY (.xtf)

Raw XTF files. Sonar data were collected November 6 to December 15, 2009, in the estuary north from Saugerties to Troy. Data Collection and Processing: The interferometric system used to measure acoustic reflectivity, provided a quantitative measure of reflectivity for every square meter of the survey area. Fugro's system measured and recorded acoustic reflectivity that has a high dynamic range such that the full range of reflectivity's encountered in the estuary environment can be recorded while maintaining a constant gain setting on the system receiver. Reflectivity data from the GeoSwath was used to produce a normalized as well as a classified image of the bottom. Additionally, Fugro provided slope, aspect and hillshade models as additional acoustic parameters. Backscatter data processing was completed with CARIS 7.0. Raw XTF files were created by converting Hypack format (*.HSX) into Triton format (*.XTF) using Hypack 2009a.

Original contact information:

Contact Name: John Ladd

Contact Org: Hudson River National Estuarine Research Reserve, NYS DEC

Phone: 845-889-4745

Email: jxLadd@gw.dec.state.ny.us

Our work was consistent with the Statement of Work prepared by the New York State Department of Environmental Conservation (NYSDEC) to develop detailed bathymetric maps, acoustic reflectivity and acoustic character maps of the shallow portions of the Hudson River Estuary from the Verrazano Narrows north to the federal dam in Troy. In addition NYSDEC requested the collection of grab samples and 100 sediment cores at least one meter in length distributed throughout the same shallow portions of the Estuary. This project was being conducted as part of the Hudson River Estuary Action Plan promulgated by NYSDEC and approved by the Governor in 1996 which committed the State to, among other things, -Conduct a submerged habitat inventory to define areas most in need of protection for Hudson River fish, blue crab, and food chain species. -To conserve, protect, and, where possible, enhance critical river and shoreline habitats to assure that the life cycles of key species are supported for human enjoyment and to sustain a healthy ecosystem. -To conserve for future generations the rich diversity of plants, animals and habitats that are key to the vitality, natural beauty and environmental quality of the Hudson River Valley. Previous work in the Estuary was limited, in that detailed bathymetry was not acquired in areas of the estuary shallower than about 4 meters due to financial constraints. About a third of the estuary was not surveyed this third is the area that is home to important submerged aquatic vegetation (SAV) beds which sustain much of the biologic community in the estuary. Utilizing advanced technology and the experience of the previous benthic mapping projects, this project provided NYSDEC maps of the shallow areas that were not addressed with the previous studies. Pilot studies (Maher, 2006; Strayer et al., 2006; Yeung and McConnaughey 2008) have indicated that variations in remote sensing acoustic data are strongly correlated to variations in benthic macro invertebrate communities. This primary goal of this project, guided by NYSDEC, was to acquire acoustic data in the shallow water areas of the estuary that would facilitate classification of the substrate into biologically significant units.

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Geographic limits of the project survey covered some or all shallow areas of the estuary from the Verrazano Narrow Bridge north to the federal dam at Troy. The landward limit of surveys along the eastern shore of the estuary was the low tide line or the railroad tracks that extend up the east shore of the estuary whichever was most westward on a given line of latitude including Schodack Creek north to Little Schodack Island. The landward limit of surveys along the western shore was the low tide line or the railroad tracks that extend up the west shore of the estuary whichever is most eastward on a given line of latitude except for tidal portions of tributaries such as the Binnen Kill north of Interstate 90 and Catskill Creek north of Bridge Street. For the purposes of this project the low-tide line was the line of zero depth relative to mean lower low water (MLLW) depicted on NOAA charts 12347 and 12348. Hypack HSX file records the digital side scan data using a 16 bit number (0-65536 data samples).

The HSX header information includes the following fields. XTFFILEHEADER: RecordingProgramName(eg. HSX2Xtf), RecordingProgramVersion(eg. 7.0), SonarName(eg.GeoAcoustics GeoSwath), ThisFileName (eg.JD335_008_1628.xtf), NoteString, NavUnits (eg.3 = "lat/long"), NumberOfSonarChannels(eg.2), NumberOfBathymetryChannels(eg.0), ProjectionType(eg.UTM83-18), SpheriodType(eg."Unknown"), ChanInfo[0].TypeOfChannel(eg.1), ChanInfo[0].ChannelName(eg."PORT"), ChanInfo[0].SubChannelNumber(eg.0), ChanInfo[0].CorrectionFlags(eg.1), ChanInfo[0].UniPolar(eg.1), ChanInfo[0].BytesPerSample(eg.2), ChanInfo[0].VoltScale(eg.5), ChanInfo[1].TypeOfChannel(eg.2), ChanInfo[1].ChannelName(eg."STBD"), ChanInfo[1].SubChannelNumber (eg.1), ChanInfo[1].CorrectionFlags(eg.1), ChanInfo[1].UniPolar(eg.1), ChanInfo[1].BytesPerSample(eg.2), ChanInfo[1].VoltScale(eg.5).

The data packet headers include Attitude (XTFATTITUDEDATA) and Sonar (XTFPINGHEADER). The time and position information is contained in the sonar header. Data was collected in UTM Zone 18 Meters. In the XTFPINGCHANHEADER structure, a substructure of the Sonar header, the number of samples is found in Offset 42 (NUMSAMPLES). The number of bytes will be this value multiplied by the number of bytes per sample. BytesPerSample found in CHANINFO structure (given in the file header).

The XTF header content is further defined by Triton in the following document - http://www.tritonimaginginc.com/site/content/public/downloads/FileFormatInfo/Xtf%20File%20Format_X26.pdf.

NOAA manages much of the data to users of digital geographic data. NOAA is in no way condoning or endorsing the application of this data for any given purpose.It is the sole responsibility of the user to determine whether or not the data is suitable for the intended purpose.It is also the obligation of the user to apply the data in an appropriate and conscientious manner.NOAA provides no warranty, nor accepts any liability occurring from any incomplete,incorrect, or misleading data, or from any incorrect, incomplete, or misleading use of the data. Much of the data is based on and maintained with ARC/GIS software developed by the Environmental Systems Research Institute (ESRI). In addition, much of the information presented uses conventions and terms popularized by ARC/GIS and its user community. NOAA in no way represents the interests of ESRI, nor acts as agents for them. In addition, New York State Department of Environmental Conservation provides these geographic data "as is." New York State Department of Environmental Conservation makes no guarantee or warranty concerning the accuracy of information contained in the geographic data. New York State DEC further makes no warranty, either expressed or implied, regarding the condition of the product or its fitness for any particular purpose. The burden for determining fitness for use lies entirely with the user. Although these data have been processed successfully on a computer system at New York State Department of Environmental Conservation, no warranty expressed or implied is made regarding the accuracy or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. This disclaimer applies both to individual use of the data and aggregate use with other data. It is strongly recommended that careful attention be paid to the contents of the metadata file associated with these data. New York State Department of Environmental Conservation shall not be held liable for improper or incorrect use of the data described and/or contained herein.

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Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 3; ESRI ArcCatalog 9.3.0.1770

Data are geo-referenced using the position data exported from the POS MV which results in a horizontal accuracy of <+/- 1 meter.

The data covers the area of the estuary north from Saugerties to Troy in areas of shallow water (defined as any part of the estuary covered by water at low tide and shallower than 5 meters relative to NAVD88). For the purpose of this project the low-tide line was the line of zero depth relative to mean lower low water (MLLW) depicted on NOAA charts 12347 and 12348.

The Kongsberg GeoSwath Plus System was used to provide swath bathymetry coverage of the riverbed in shallow water. The system uses interferometric sonar, generating short pulses of acoustic energy which propagate out from the transducers at the speed of sound in water, ensonifying a narrow strip of riverbed perpendicular to the vessel track. Side scan data was collected utilizing the GeoSwath's backscatter at 255 kHz.

For positioning, Fugro conducted the survey operations using a combination of DGPS and PPK. The differentially corrected position from DGPS was transmitted to the POS MV (Position Orientation System for Marine Vessels) via ethernet at 25 Hz and recorded to a POS file to be processed in conjunction with the base station data. Final corrected positions are accurate to <+/- 1 meter.

Geoswath and position data from the POS MV was recorded in Hypack 2009a.